Many of the current shortcomings in diagnosis, prognosis, risk stratification and treatment of disease can be approached through the identification of the molecular mechanisms underlying a disease and through the discovery of nucleotide sequences (or sets of nucleotide sequences) whose expression patterns predict the occurrence or progression of disease states, or predict a patient's response to a particular therapeutic intervention. In particular, identification of nucleotide sequences and sets of nucleotide sequences with such predictive value from cells and tissues that are readily accessible would be extremely valuable. For example, peripheral blood is attainable from all patients and can easily be obtained at multiple time points at low cost. This is a desirable contrast to most other cell and tissue types, which are less readily accessible, or accessible only through invasive and aversive procedures. In addition, the various cell types present in circulating blood are ideal for expression profiling experiments as the many cell types in the blood specimen can be easily separated if desired prior to analysis of gene expression. While blood provides a very attractive substrate for the study of diseases using expression profiling techniques, and for the development of diagnostic technologies and the identification of therapeutic targets, the value of expression profiling in blood samples rests on the degree to which changes in gene expression in these cell types are associated with a predisposition to, and pathogenesis and progression of a disease.
There is an extensive literature supporting the role of leukocytes, e.g., T- and B-lymphocytes, monocytes and granulocytes, including neutrophils, in a wide range of disease processes, including such broad classes as cardiovascular diseases, inflammatory, autoimmune and rheumatic diseases, infectious diseases, transplant rejection, cancer and malignancy, and endocrine diseases.
Of particular interest is the role of leukocytes and leukocyte gene expression in chronic inflammatory diseases such as Systemic Lupus Erythematosis and Rheumatoid Arthritis. Systemic lupus erythematosis (SLE) and Rheumatoid Arthritis (RA) are chonic autoimmune and inflammatory disorders characterized by dysregulation of the immune system, which causes damage to a variety of organs. These diseases clearly involve differential expression of genes in leukocytes. Diagnostic and disease monitoring tools are severly lacking for these patients and their physicians. Leukocyte expression profiling can be applied to discover expression markers for SLE and RA and apply them as patient management tools in the clinical setting. In addition, osteoarthirtis is a degenerative joint disease that can be confused with RA. This disease also involves leukocytes and expression profiling of leukocytes associated with osteoarthritis may lead to the discovery of new diagnostic and therapeutic approaches to the disease.
The accuracy of technologies based on expression profiling for the diagnosis, prognosis, and monitoring of disease would be dramatically increased if numerous differentially expressed nucleotide sequences, each with a measure of sensitivity and specificity for a disease in question, could be identified and assayed in a concerted manner. Using the expression of multiple genes (gene sets) for diagnostic applications helps overcome assay and population variability. In order to achieve this improved accuracy, the appropriate sets of nucleotide sequences need to be identified and validated against numerous samples in combination with relevant clinical data.